1. Field of the Invention
The present invention relates to a liquid atomizing nozzle, and more particularly to a liquid fuel atomizing nozzle to be used in a combustion chamber of a jet engine, gas turbine or the like, by an air stream of air or the like.
2. Description of the Related Art
As one means for atomizing liquids, there are air-blast liquid fuel atomizing nozzles which atomize liquid fuel by means of an air blast, which have come to be used in recent jet engines and liquid fueled gas turbines. Air-blast liquid fuel atomizing nozzles are a form of nozzle wherein liquid fuel is atomized by means of an air blast which flows into a combustion chamber. The liquid fuel is supplied in the form of a liquid film, and as a result of this thin liquid film contacting with an air stream having a speed of several tens of meters per second, is atomized from the front end edge of the nozzle into free space. Atomization is facilitated by supplying liquid fuel in a liquid film.
FIG. 4 is a diagram which shows one example of the structure of a typical air-blast liquid fuel atomizing nozzle of the liquid film method. FIG. 4(a) is a longitudinal sectional view thereof, FIG. 4(b) is a B4xe2x80x94B4 sectional view of (a), FIG. 4(c) is a C4xe2x80x94C4 sectional view of (a), and FIG. 4(d) is a D4xe2x80x94D4 sectional view of (a). The air-blast liquid fuel atomizing nozzle 30 (hereafter abbreviated as xe2x80x9catomizing nozzlexe2x80x9d) shown in FIG. 4 comprises a tapered outer cylinder 32 which is formed with a progressively thin-walled front end section, and an inner cylinder 33 which is arranged within the outer cylinder 32 in a condition extending along the same axis. An annular space 37 which is open towards the front end side is formed between the inner wall surface 35 of the outer cylinder 32 and the outer wall surface 36 of the inner cylinder 33. The annular space 37 is formed in a conical shape of a reducing diameter towards the front end side. The outer cylinder 32 and the inner cylinder 33 connect at a cylindrical nozzle base 34 in the back end.
The back end section of nozzle base 34 is connected to a pipe 40 to receive a supply of a liquid fuel LF to be atomized, and the liquid fuel LF supplied though the pipe 40 passes through a passage 41 formed within the nozzle base 34 and flows into an annular liquid reservoir 42 formed within the same nozzle base 34. The liquid reservoir 42 and the annular space 37, as is shown in FIG. 4(d) in particular, connect through a plurality of spiral passages 43 which are formed in parallel to each other. The liquid fuel LF which has flowed into the annular space 37 from the spiral passages 43, flows and forms a liquid film FF over the inner wall surface 35 of the outer cylinder 32, and is atomized from a front end edge 44 arising from the thin wall of the outer cylinder 32 and flows out into free space.
The liquid fuel LF is given a rotating motion by being passed through the spiral passages 43, and this rotation produces an action of inducing a spreading and moreover stabilization and the like in the liquid film FF on the inner wall surface 35 of the outer cylinder 32. The part of the atomizing nozzle 30 that forms the liquid film FF is called a prefilmer (liquid film forming section) 45. Along an outer wall surface (the outer wall surface of the outer cylinder 32) 46 and an inner wall surface (the inner wall surface of the inner cylinder 33) 47 of the prefilmer 45, air is flowing into a combustion chamber (the air streams Ao, Ai). Most commonly, a rotating motion is given to the air streams Ao, Ai which flow through the passages within and without the prefilmer 45 by swirl vanes 48,49 in order to facilitate mixing of air and fuel particles that have been atomized and in order to stabilize the flame within the combustion chamber. The liquid film FF is atomized largely through air encountering these, namely an air stream Ai flowing along the inner wall surface 47, but the rotation of the air stream Ai on this inner side is also effective in stabilizing the liquid film FF on the prefilmer 45. The air stream Ao which flows along the outer wall surface 46 of the prefilmer 45 also produces an action which prevents liquid from running back from the front end edge 44 to the outer wall surface 46, and prevents bulking of the liquid fuel particles which are atomized from the front end edge 44.
With air-blast liquid fuel atomizing nozzles, it is important to make the properties of the spray resulting from the fuel particles which have been atomized symmetrically around the axis of the nozzle. If there are deviations in the fuel concentration in the circumferential direction around the axis of the nozzle, due to differences in the ratio of fuel and air (air-fuel ratio) according to the position around the axis of the nozzle, the flame stability is impaired, producing deviations in the temperature distribution within the combustion chamber, and as a result, high temperature combustion or locally incomplete combustion occurs, giving rise to problems of increased generation of harmful components or incompletely combusted components.
In the atomizing nozzle 30 shown in FIG. 4, due to the spiral passages 43 or the liquid passages corresponding thereto being set located apart in the circumferential direction, there is a tendency for the thickness of the liquid film FF to become thick in positions around the circumference which correspond to the spiral passages 43 or the liquid passages, even on the prefilmer 45. In cases where the number of the spiral passages 43 is low or the axial length of the prefilmer 45 is short, this tendency is particularly pronounced. Easing this problem by making the annular space 37 an extremely narrow annulus could be considered, but in cases which adopt this kind of measure, the liquid fuel cannot be given rotation. Moreover, when attempting to resolve this problem by making the cross-sectional area of the spiral passages 43 smaller and in exchange increasing the number of the spiral passages 43, another problem occurs of passage blockages developing easily as a result of solid deposits in the liquid fuel.
Furthermore, in times of low fuel flow rates, there is a tendency for the flow rate of fuel passing through the spiral passages 43 in the bottom side to become larger than in the upper side due to pressure differences in the top and bottom of the liquid reservoir 42 resulting from gravitational force, and due to this a problem occurs in which the fuel discharge volume of the atomizing nozzle 30 deviates in the circumferential direction. There are also cases where these kind of deviations can be eased by reducing the cross-sectional area of the spiral passages 43 and by applying adequately high pressure to the fuel in liquid reservoir 42 so that pressure differences which occur through gravitational force can be ignored, but in many cases elevation of the fuel pressure is restrained by problems such the above-mentioned blockages through solid deposits or fuel flow rate turndown ratios (the maximum fuel flow rate of an engine divided by the minimum fuel flow rate).
The strongest controlling factor on the size of the droplets formed by means of atomization is the thickness of the liquid film, and in the development of air-blast liquid atomizing nozzles, efforts have been focused on how to form a thin liquid film which is furthermore uniform around the circumference. If the liquid film becomes thick, even locally, the larger droplets generated there become, and in a case of liquid fuel may be tied to outbreaks of smoke-generation or incomplete combustion. In order to avoid these drawbacks in combustion which are ascribable to deviations in fuel concentration, it is essential to disperse the liquid fuel as uniformly as possible in the circumferential direction around the nozzle axis.
Consequently, in air-blast liquid atomizing nozzles, dispersing the liquid as much as possible uniformly in the circumferential direction of the nozzle, namely, forming a liquid film which is as much as possible uniformly thin in the circumferential direction of the nozzle axis, and facilitating further the atomization of the liquid is a problem that has to be resolved. In the case of a liquid fuel, if the air which flows into the combustor can be utilized to make the liquid film uniform, it can be expected to be useful in simplifying the structure.
An object of this invention is to provide a novel liquid atomizing nozzle which further facilitates the atomization of liquid, and dramatically improves uniformity in the circumferential direction and furthermore reduces the thickness of a liquid film, in order to solve the above problems in an air-blast liquid atomizing nozzle which disperses a liquid film with an air blast.
In order to solve the above problems, a liquid atomizing nozzle comprises an outer member, and an inner member which is arranged within the outer member and forms an annular space which is open towards a front end side with the outer member, so that a liquid that has been injected into the annular space is atomized from the front end of the outer member, and in this liquid atomizing nozzle the outer member is provided with liquid passages inclined to the radial direction and for injecting the liquid into the annular space, and at least one of the outer member and the inner member is provided with gas passages that are opening to the annular space and are inclined to the radial direction in order to swirl a gas in the same direction as the flow direction of the liquid that has been injected into the annular space.
According to this liquid atomizing nozzle, the liquid which is injected into the annular space through the liquid passages formed in the outer member flows within the annular space interior having a component swirling in the circumferential direction because the liquid passages are formed inclining to the radial direction. Because the gas passages in at least one of the above outer and inner members which are formed in a condition opening into the annular space are also formed inclining to the radial direction, the gas which flows into the annular space generates a swirling flow within the annular space. However, because the direction of this swirling flow is the same with the direction of the liquid in the annular space which has been injected from the liquid passages, through the swirling flow of the gas, an injected liquid flow which flows within the annular space is efficiently spread over the surface of the inner wall of the outer member as a liquid film. In other words, the strong swirling flow of the gas which flows into the annular space is utilized, so that even in a case where there are deviations in the outflow of liquid to the annular space interior, through the swirling flow of the gas, thick sections of the liquid film flow and spread out circumferentially to thin sections of the liquid film, and the thickness of the liquid film is made uniform in the circumferential direction.
Furthermore, even in a case where the flow rate of the liquid is low and there are large deviations in the circumferential direction in the outflow of liquid from the liquid passages which connect to the liquid reservoir, the liquid is spread in the circumferential direction by the swirling flow of the gas within the annular space. Accordingly, the liquid film which has been extended is atomized in small droplets from the front end edge of the outer member, and atomization is promoted. Additionally, because this liquid atomizing nozzle does not require the cross sections of the discharge passages of the liquid to be reduced, it may be applied to liquids in which solid deposits develop easily through rises in temperature, as can be seen in fuels such as heavy oils and the like. The gas passages may be formed in either or both the inner and outer members, but from the standpoint of swirling flow, which becomes stronger as the swirling radius becomes smaller, and the size-reduction and the like of liquid atomizing nozzles, forming the gas passages in the outer member is desirable.
In this liquid atomizing nozzle, the above gas passages can be made to be open in a condition tangential to the circumference of the inner wall surface of the above outer member. By constructing the gas passages in this way, the gas which has passed through the gas passages inflows in a tangential direction to the annular space and a strong swirling flow can be efficiently formed. In this case, the incline to the radial direction of the gas passages becomes a right angle. As a configuration to make the gas passages be open in a condition tangential to the circumference of the annular space, the wall surface which forms the gas passages, for example a part of the wall surface which has a rectangular cross section, can be placed within a plane tangential to the inner wall of the outer member.
Furthermore, in this liquid atomizing nozzle, the above liquid passages can be made to be open in a condition tangential to the circumference of the inner wall surface of the above outer member. By constructing the liquid passages in this way, the liquid which has passed through the liquid passages inflows in a tangential direction to the inner wall surface of the outer member forming the annular space, and the uniformity of the thickness of the liquid film which is formed on the inner wall surface can be improved. As a configuration to make the liquid passages be open in a condition tangential to the circumference of the annular space, the wall surface which forms the liquid passages, for example a part of the wall surface which has a rectangular cross section, can be placed within a plane tangential to the inner wall of the outer member.
In this liquid atomizing nozzle, it is desirable that the above liquid passages and the above gas passages are made to be open into the above annular space alternately in the circumferential direction. By forming the liquid passages and the gas passages in this way, any liquid whatsoever which has passed through the liquid passages and been injected into the annular space will be spread more uniformly on the inner wall of the outer member through the swirling flow of the gas flowing into the annular space through the gas passages, and the thickness of the liquid film can be made circumferentially uniform.
In this liquid atomizing nozzle, as viewed in the direction of the axis of the above liquid atomizing nozzle, the above gas passages can be made to be open within the above annular space in essentially the same position as the above liquid passages are open in the annular space or in a position further to the rear side than this. By injecting the gas before the liquid and forming a swirling flow, and injecting the liquid into this swirling flow, or injecting the gas and the liquid in essentially the same position as viewed in the direction of the nozzle axis of the liquid atomizing nozzle, the extension of the liquid over the surface of the inner wall of the outer member can be made all the more uniform.
In this liquid atomizing nozzle, the outer member may be a tapered cylinder in which the front end is thin walled, and an inner cylinder which is disposed on the same axis as the above outer cylinder and is connected at the rear side through the inside of which air stream flow which atomizes the above liquid at the front end of the above annular space. The liquid injected in the annular space is atomized from the front end of the tapered outer cylinder by the air stream flowing through the interior of the inner cylinder and disperses.
In this liquid atomizing nozzle, swirlers may be provided in at least one of the areas consisting of the interior of the above inner cylinder or the exterior of the above outer cylinder for giving swirling movement to the gas stream flowing along the above-mentioned interior or the above-mentioned exterior. As a result of providing swirlers, the flow of the gas which has been given swirling movement flows to the outer side or inner side of the prefilmer that forms a liquid film. The rotating gas which flows on the inner side of the prefilmer facilitates further the atomizing of the droplets when the liquid film of the liquid membrane is disintegrated at the front end edge of the outer cylinder, and the rotating gas flow which flows on the outer side of the prefilmer may preventing liquid particles that are atomized from the front end edge from getting large in size.